This invention relates to an apparatus and method for commercially producing sheets of dough and more particularly, for producing "stress free" sheets of dough. "Stress free" dough is dough which has not had the gluten of the dough fractured or damaged in the sheeting process.
The current practice for commercially producing sheets of dough by a batch method generally involves measuring the required dry ingredients (i.e., flour, sugar, yeast, etc.) and mixing them with the appropriately measured liquid ingredients (i.e., water, oil, etc.). The resulting dough paste created by mixing of these ingredients is then kneaded until the desired dough mass containing the gluten network is formed. The dough mass is then typically transferred to a retention hopper or bin and commingled with previously prepared batches of dough from which the dough mass is extruded by a combination of peripherally ribbed oppositely rotating discharge rollers which force the dough mass through an extrusion die or restricted opening to form a continuous stream of dough. In the course of forcing the dough through the extrusion die, the discharge rollers forcefully pull small portions of the dough from the large dough mass in the retention bin and push it through the die or restricted opening to form the continuous stream of extruded dough. Once extruded, the stream of dough can be shaped, rolled, or cut to the desired specifications depending on the ultimate dough product (i.e., croissant, bread loaf, bun, pizza crust, etc.).
As the dough is kneaded or worked during the kneading process, the gluten network is generated in the dough. The gluten network is a highly elastic and cohesive gel structure which is generally indicative of the quality of the dough. The more developed and undamaged the gluten network remains in the dough, the higher the quality of the resulting dough product. Gluten in the dough is damaged or destroyed as a result of high stresses or shear forces applied to the dough. Therefore, the less stress imparted to the dough or the more "stress free" the dough remains during the formation of a dough stream, the higher the quality of the resulting dough product.
In the practice of the above described commercial process for producing a continuous sheet of dough, peripherally ribbed discharge rollers which pull the dough from the retention bin and force it into the extrusion die exert a significant shear or tearing force on the dough. These shear forces greatly damage and destroy the gluten network. Additionally, the mechanical work energy of the discharge rollers applied to the dough in the course of shearing it from the dough mass and forcing it through the extrusion die, increases the temperature of the dough by as much as 5.degree. F. This temperature increase further damages the dough.
In addition to the damage to the dough mass imparted by the shear stress and the increase in temperature of the dough, the compression forces applied to the dough by the discharge rollers further damage the dough. The resulting stream of compressed dough emerging from the extrusion die is difficult to shape and form because of these compression forces. The damaged dough can be partially restored if passed through a series of rollers and shapers, but this corrective measure is much more timely and costly than if the dough had never been compressed and the gluten network damaged in the first place. An additional corrective measure common in the industry to rehabilitate compressed dough and the damaged gluten network thereof is to leave the dough to rest for as much as two hours after extrusion from the retention bin. Once again, this practice serves to only partially regenerate the gluten and is inherently time consuming and a further complicating requirement to produce a continuous sheet of quality stress free dough. The dough which has been rehabilitated is still of a lesser quality and resistant to shaping than "stress free" dough.
There are prior patents directed to methods and apparatus for producing a continuous stream of stress free dough. U.S. Pat. No. 5,091,202, for example, discloses a dough hopper with a pair of vertically mounted conveyors and a pair of discharge rollers positioned below an opening in the bottom of the hopper. The continuous stream of dough is produced according to the disclosure of this patent by pulling the dough out of the hopper opening and sandwiching it between the conveyors and then the discharge rollers. The dough is flattened and narrowed to achieve a stream of dough by controlling the cross-sectional area between the conveyors and between the rollers and regulating their respective rotational velocities. However, the gluten is still damaged with such a method due to the compressive forces between the conveyors and rollers and the work energy converted to heat energy when applied to the dough by the conveyor and roller rotation.
Similarly, U.S. Pat. No. 4,276,317 discloses a method for producing a strip of dough by means of a plurality of opposing pairs of discharge rollers positioned below a dough hopper. The rollers form the strip of dough by reducing the spacing between each successive pair of discharge rollers thereby flattening the dough as it passes between the rollers. The resulting dough stream generated by the practice of this patent is also not truly stress free due to the compressive forces and the temperature rise experienced by the dough according to the practice of this patent.
Another method for producing a continuous stream of "stress free" dough is disclosed in U.S. Pat. No. 4,904,491 in which the dough is severed into portions by cutter blades at the bottom of a dough hopper. The blades section the dough into individual portions which are weighed and placed on a conveyor to occupy a space proportional to its mass. The speed of the conveyor is controlled to correspond to the mess of each portion of dough and each successive portion is positioned to overlap the previous portion, thereby forming a continuous stream of dough when rolled and shaped appropriately. Although gluten damaging excessive pressures are reduced, the involved steps of weighing each portion of dough and regulating the conveyor to overlap each portion complicate the dough stream production. In addition, cutting the dough into individual portions severs the gluten network formed in the dough thereby requiring reformation of the gluten network when the dough is ultimately formed into a stream.
The so called "stress free" systems described in the above identified patents are all based on a batch process where the dough is mixed and kneaded in a batch mixer. Batch sizes can vary from as little as 100 pounds to as much as 2,000 pounds per batch.
In the time frame of starting and finishing the use of the batch, time lapses of up to 20 minutes are common. The dough structure changes due to continuing moisture absorption, development of yeast and relaxation of gluten during this time frame. This results in changes of quality from beginning to end of batch, as well as changes of consistency and workability of the dough.
This inconsistency requires specialized, automated sheeting systems to produce a more consistent finished product. The invention of this application mixes and kneads the dough continuously which results in consistent dough throughout the process since each dough particle has the same mix time, knead time and rest time.
The system of this invention makes it possible to use lower amounts of yeast, since lapse times between mixing and finishing the final product can be as little as two minutes, which results in very little to no yeast development. This is a big advantage, particularly for frozen dough products.